C Preprocessor Error Macro
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message. You would use ‘#error’ inside of c preprocessor macro arguments a conditional that detects a combination of c preprocessor macro tricks parameters which you know the program does not properly support. For
C Preprocessor Macro Variable Arguments
example, if you know that the program will not run properly on a VAX, you might write #ifdef __vax__
C Preprocessor Macro Concatenation
#error "Won't work on VAXen. See comments at get_last_object." #endif If you have several configuration parameters that must be set up by the installation in a consistent way, you can use conditionals to detect an inconsistency and report c preprocessor macro overloading it with ‘#error’. For example, #if !defined(FOO) && defined(BAR) #error "BAR requires FOO." #endif The directive ‘#warning’ is like ‘#error’, but causes the preprocessor to issue a warning and continue preprocessing. The tokens following ‘#warning’ are used as the warning message. You might use ‘#warning’ in obsolete header files, with a message directing the user to the header file which should be used instead. Neither ‘#error’ nor ‘#warning’ macro-expands its argument. Internal whitespace sequences are each replaced with a single space. The line must consist of complete tokens. It is wisest to make the argument of these directives be a single string constant; this avoids problems with apostrophes and the like.
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C Preprocessor Macro If
APIs and reference Dev centers Retired content Samples We’re sorry. The c preprocessor macro in string content you requested has been removed. You’ll be auto redirected in 1 second. C/C++ Preprocessor Reference Preprocessor Preprocessor c preprocessor macro recursion Directives Preprocessor Directives #error Directive #error Directive #error Directive #define Directive #error Directive #if, #elif, #else, and #endif Directives #ifdef and #ifndef Directives #import Directive #include Directive #line Directive https://gcc.gnu.org/onlinedocs/cpp/Diagnostics.html Null Directive #undef Directive #using Directive TOC Collapse the table of content Expand the table of content This documentation is archived and is not being maintained. This documentation is archived and is not being maintained. #error Directive (C/C++) Visual Studio 2015 Other Versions Visual Studio 2013 Visual Studio 2012 Visual Studio 2010 Visual Studio 2008 Visual Studio 2005 Visual https://msdn.microsoft.com/en-us/library/c8tk0xsk.aspx Studio .NET 2003 The #error directive emits a user-specified error message at compile time and then terminates the compilation.Syntax Copy #errortoken-string RemarksThe error message that this directive emits includes the token-string parameter. The token-string parameter is not subject to macro expansion. This directive is most useful during preprocessing for notifying the developer of a program inconsistency or the violation of a constraint. The following example demonstrates error processing during preprocessing: Copy #if !defined(__cplusplus) #error C++ compiler required. #endif See AlsoPreprocessor Directives Show: Inherited Protected Print Export (0) Print Export (0) Share IN THIS ARTICLE Is this page helpful? Yes No Additional feedback? 1500 characters remaining Submit Skip this Thank you! We appreciate your feedback. Dev centers Windows Office Visual Studio Microsoft Azure More... Learning resources Microsoft Virtual Academy Channel 9 MSDN Magazine Community Forums Blogs Codeplex Support Self support Programs BizSpark (for startups) Microsoft Imagine (for students) United States (English) Newsletter Privacy & cookies Terms of use Trademarks © 2016 Microsoft © 2016 Microsoft
article is written like a manual or guidebook. Please help rewrite this article from a descriptive, neutral point of view, and remove advice or instruction. (February 2013) (Learn how and https://en.wikipedia.org/wiki/C_preprocessor when to remove this template message) This article includes a list of references, but http://www.complete-concrete-concise.com/programming/c/preprocessor-%E2%80%93-the-error-directive its sources remain unclear because it has insufficient inline citations. Please help to improve this article by introducing more precise citations. (March 2015) (Learn how and when to remove this template message) (Learn how and when to remove this template message) The C preprocessor or cpp is the macro preprocessor for the C c preprocessor and C++ computer programming languages. The preprocessor provides the ability for the inclusion of header files, macro expansions, conditional compilation, and line control. In many C implementations, it is a separate program invoked by the compiler as the first part of translation. The language of preprocessor directives is only weakly related to the grammar of C, and so is sometimes used to process other kinds of text files. c preprocessor macro Contents 1 Phases 1.1 Including files 1.2 Conditional compilation 1.3 Macro definition and expansion 1.4 Special macros and directives 1.4.1 Token stringification 1.4.2 Token concatenation 1.5 User-defined compilation errors 2 Implementations 2.1 Compiler-specific preprocessor features 3 Other uses 4 See also 5 References 6 External links Phases[edit] Preprocessing is defined by the first four (of eight) phases of translation specified in the C Standard. Trigraph replacement: The preprocessor replaces trigraph sequences with the characters they represent. Line splicing: Physical source lines that are continued with escaped newline sequences are spliced to form logical lines. Tokenization: The preprocessor breaks the result into preprocessing tokens and whitespace. It replaces comments with whitespace. Macro expansion and directive handling: Preprocessing directive lines, including file inclusion and conditional compilation, are executed. The preprocessor simultaneously expands macros and, in the 1999 version of the C standard,[clarification needed] handles _Pragma operators. Including files[edit] One of the most common uses of the preprocessor is to include another file: #include
and often underused preprocessor directive. Behaviour of this preprocessor directive is the same for both C and C++ compilers. Purpose The #error directive terminates compilation and outputs the text following the directive. Format #error text All preprocessor directives begin with the # symbol. It must be the first character on the line or the first character on the line following optional white space. Some early compilers flagged an error if # was not the first character on the line. Spaces or tabs are permitted between the # and error, but not escape characters or other symbols or macros. The preprocessor removes white space and concatenates the # and error together. If anything follows the #error directive (other than white space) then the program is malformed. The following are valid uses: #error some error message text # error some error text to display # /* comments are white space */ error some error message to display The following are invalid uses: // #\ is not a valid preprocessor directive # \t error text to output // #" is not a valid preprocessor directive # "" text to output Use It is used to render a program malformed and output the text following the #error directive. The text may be quoted or unquoted (it doesn't matter). No macro expansion takes place. The language specifications do not say how the text following the #error directive is to be treated. The GCC compiler, replaces all white space characters between tokens with a single white space character. I have no reason to believe other compilers behave differently since white space is not considered significant in the C and C++ languages - it serves only to seperate tokens from one another. There are many times when it is useful to halt compilation: code is incomplete code requires particular library versions code uses compiler dependent features code has specific compiler requirements Incomplete Code When developing code, it is common to create stub functions. For the final release, these stub functions need to be implemented. We can let the compiler help us catch unimplemented functions: int my_